A screw of this type is already known, in particular from GB-A-898 026. The breakable neck is suitable for shearing during tightening, when the tightening torque reaches a predetermined value corresponding to the minimum diameter of the neck. The second head, which is closer to the shank, can nevertheless still be used to remove and optionally replace the screw.
Breaking of the neck, i.e. severing of the first head from the remainder of the screw, serves to avoid any excessive tightening.
When the first head is severed, nothing is provided to retain it, so it merely falls to the ground.
In particular because of the danger that might result therefrom, it is not acceptable for screw heads to be left lying on the floor of an assembly workshop, so workers regularly have to pick them up. The fact that these heads fall to the floor thus has the consequence of impeding and slowing down the work done.